(def func #(- (* % % %) 1))
(def func' #(* 3 (* % %)))
(def eps 1e-8)

(defn eps-eq? [a b] (> eps (abs (- a b))))
(defn eps-zero? [a] (eps-eq? a 0))
(defn eps-root? [a] (eps-zero? (func a)))

(defn n-iterations [start n]
  (reduce (fn [x _]
            (if (eps-root? x)
              (reduced x)
              (- x (/ (func x) (func' x)))))
          start
          (range n)))